The present invention is directed to a fire resistant ceiling supporting system particularly useful for supporting a drywall ceiling. The system is capable of absorbing thermal expansion without any substantial buckling of the members so that the drywall ceiling will not collapse during abnormal elevated temperatures thereby preserving the integrity of the ceiling as a barrier under fire conditions.
A fire rated drywall ceiling support system is disclosed in U.S. Pat. No. 4,208,851. In this system, main runners, which are substantially a T-shaped member having a bead along one edge of a web and flanges on the opposite edge, are spliced together with a particular splice that allows for compensation of thermal expansion of the main runners caused by fire. The relief of the thermal expansion occurs in the area of the splice.
This system also has channel-shaped cross members extending between the main runners on which the drywall can be secured. These cross members have a channel-shaped member with upstanding side walls with outwardly extending flanges, with the flanges being provided with notches. The ends of the flanges are inserted into the main runner with the notch receiving or engaging the web. Due to a cam base of the notch, expansion is compensated by the cross channel extending further into the apertures of the web. However, a firm, stable construction is not always present.